Electrical information storage system

ABSTRACT

An electrical information or latent image storage system using a storage element which comprises a layer of substantially electrically insulating material having a layer of electrically photosensitive particulate material embedded therein, with a layer of semiconductor material overcoating one surface of the layer of insulating material, and an electrode on the opposite surface of the layer of insulating material. Information in the form of localized electrical charges of an electrical latent image is placed on the element by electrical or photo-electrical means, the information can be retrieved by scanning the element using an electrode-pair grid pattern, an electron beam, or other suitable means, and the retrieved information may be used, for example, through a computer, or reconstructed into a visible image corresponding to a latent image.

This is a division of application Ser. No. 539,913, filed Jan. 9, 1975,now allowed.

A variety of information storage and retrieval systems are known and nowin use. For example, digital computers store and retrieve binaryinformation from storage register memories, or magnetic core memories.Analog computers store and retrieve information in the form of varyingvoltage levels. Information is also stored and retrieved in variousmagnetic tape or magnetic card storage and retrieval systems. Inaddition to the foregoing electrical and magnetic systems, more familarforms of information storage and retrieval systems include printedpaper, film, and microfilm, all of which may have information storedtherein by any of a variety of mechanical, chemical, photochemical, orphotoelectrical means.

A recently developed example of an electrically or photoelectricallyaddressable microfilm system is a migration imaging system capable ofproducing high quality images of high density, continuous tone, and highresolution. Such a migration imaging system is disclosed, for example,in Goffe U.S. Pat. Nos. 3,520,681, 3,801,314, and in copendingapplication Ser. No. 837,591, filed June 30, l969 now U.S. Pat. No.4,013,462. In a typical embodiment of this migration imaging system, animaging member which comprises a substrate, a layer of softenablematerial, and a layer of photosensitive marking material, iselectrically latently imaged by electrically charging the member, andexposing the charged member to a pattern of activating electromagneticradiation, such as light. Where the photosensitive marking material wasoriginally in the form of a layer thereof contiguous the upper surfaceof the softenable layer, marking particles in the exposed areas of themember typically migrate toward the substrate when the member isdeveloped by softening the softenable layer.

There have also been found methods for capturing or setting anelectrical latent image provided in imaging members such as those usedin the aforementioned migration imaging system, either by storing thelatently imaged member in the dark, or by applying heat, vapor, orpartial solvents, in a partial softening step to thereby capture or setthe electrical latent image. Such image setting systems are disclosed,for example, in copending applications Ser. Nos. 349,585; 349,506; and349,505; all filed Apr. 9, 1973.

Despite the technical progress in information storage and retrieval, andparticularly in electrically generated information storage and retrievalsystems as indicated above, there is still a need for improved and moreeconomical systems for storing and retrieving electrical information andelectrical latent images. For example, the memory systems used indigital computer applications are typically expensive components oftenrequiring a great deal of microcircuitry which requires much use andreuse in order to make such units economically feasible. While magnetictape or card systems are typically used for voice recording, recordingof typewritten information, and recording of digital information, thesemagnetic systems are typically not used for storing and retrievingphotographic-type imaged information. In the advantageous migrationimaging system described above, while certain methods preserving latentimages are known, there continues to be a need for increasing theability to store such electrical latent images, and to date no reallysatisfactory method of reading out electrical latent images in suchmigration imaging members, without physically developing the latentimages into visable images on the same member, has been realized.

As mentioned above, the present known systems for storing photographicimages which are readily retrievable by electronic means, tend to bevery expensive. Because a vary large number of individual bits ofinformation are required for storing a reasonably good quality image,and because of the need to assign certain tonal contrast information toeach bit, the only practical presently known way to electronically storesuch information is on magnetic tape, which provides a large area inwhich to store such large quantities of information. Photographic filmand printed paper are much more efficient mediums which to store opticalimages, particularly with respect to capacity (quantity of informationper unit area) and tonal fidelity. But photographic images on paper orfilm are quite awkward to electronically retrieve. While electroopticdevices have been developed for such applications, these devices whichprovide on interface between the optical image and correspondingelectronic signals typically degrade the quality of the optical imageinformation. The present invention provides a new form of photographicimage storage system which combines the advantages of optical imagestorage in photographic film or paper, with the simple, fast retrievalcapabilities of media like magnetic tape.

BRIEF SUMMARY OF THE INVENTION

It is, therefore, an object of this invention to provide an electricalinformation storage and retrieval system which overcomes the above-noteddisadvantages and fulfills the aforementioned needs.

It is another object of this invention to provide novel electricalinformation storage members.

It is another object of this invention to provide an electricalinformation and storage member from which the electrical information maybe retrieved, without physically changing the make-up of the storagemember or visibly indicating the information on the storage member.

It is another object of this invention to provide a system and memberfor permanent storage of electrical information and electrical latentimages in typical room environments.

It is another object of this invention to provide a novel system forstoring and retrieving electrical information and electrical latentimages.

It is another object of this invention to provide a system whereinadditional electrical information may be added to that already on anelectrical information storage member.

It is a further object of this invention to provide a system for quicklyreading out electrical information from an electrical informationstorage member.

It is still another object of this invention to provide an economicalelectrical information storage member which may be used in relativelytemporary applications after which it is disposable.

The foregoing objects and others are accomplished in accordance with thepresent invention which is an electrical information or latent imagestorage system using a storage element comprising a layer ofsubstantially electrically insulating material having a layer ofelectrically photosensitive particulate material embedded therein, witha layer of semiconductor material overcoating one surface of the layerof insulating material, and an electrode on the opposite surface of thelayer of insulating material. Information in the form of localizedelectrical charges or an electrical latent image is placed on theelement by electrical or photo-electrical means. That information can beretrieved by scanning the element using an electrodepair grid pattern,an electron beam, or any other suitable means. The retrieved informationmay then be used, for example in further computer applications orreconstructed into a visible image corresponding to any latent image.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention as well as other objects andfurther features thereof, reference is made to the following detaileddisclosure of preferred embodiments of the invention taken inconjunction with the accompanying drawings thereof, wherein:

FIG. 1 is a partially schematic, cross-sectional view of theadvantageous electrical information storage members of the presentinvention.

FIG. 2 is a partially schematic, cross-sectional view of an embodimentof the advantageous electrical information storage members of thepresent invention including a plurality of electrode pairs for use inaddressing and/or reading out information from the member.

FIGS. 3A, 3B, and 3C are partially schematic, magnified area views ofthe surface of the member of FIG. 2 showing various configurations ofthe electrode pairs.

FIGS. 4A-4C are partially schematic, cross-sectional views of theelectrical information storage member of FIG. 2, showing steps includingselectively exposing portions of the member with activatingelectromagnetic radiation to create an electrical latent image in themember.

FIG. 5 is a partially schematic, cross-sectional view of a member likethat illustrated in FIG. 2 further schematically illustrating a systemfor retrieving electrical information from an area of the member whereinsuch information is stored.

FIGS. 6A-6C are partially schematic, cross-sectional views of theelectrical information storage member of FIG. 2, showing steps includingselectively electrically addressing the member while it is uniformlyexposed with activating electromagnetic radiation to create anelectrical latent image in the member.

FIG. 7 is a partially schematic, cross-sectional view of anotherpreferred embodiment of the electrical information storage members ofthe present invention.

FIG. 8 is a partially schematic, cross-sectional view of anotherpreferred embodiment of the advantageous electrical information storagemembers of the present invention, additionally schematicallyillustrating another preferred system for retrieving information fromthe information storage member.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The advantageous electrical information storage members of the presentinvention are illustrated in FIG. 1, where member 10 comprises a layerof substantially electrically insulating material 11 containing a layerof electrically photosensitive particulate material 12, with a layer ofconductive electrode material 13 in contact with one surface of thelayer of electrically insulating material 11, and a layer ofsemiconductor material 14 in contact with the opposite surface of thelayer of insulating material 11. The electrical information storagemember of the present invention, primarily comprises the insulatinglayer 11, photosensitive material 12 and semiconductor layer 14, andthose elements are usually accompanied by electrode 13. The storagemember 10 may, and typically will be supported by a substrate 15a or15b. In FIG. 1, substrate 15a is shown supporting the member with thesemiconductor layer 14 in contact with the substrate 15a, while analternative embodiment may comprise the conductive electrode material 13of member 10 in contact with a substrate 15b. In various embodiments,one or both of the substrates 15a and/or 15b may be used in conjunctionwith the storage member 10. As shown in FIG. 1, the layer ofelectrically photosensitive particulate material 12, preferably is inthe form of a monolayer spaced apart from both the top surface of layerof electrically insulating material 11 and from the layer ofsemiconductor material 14. However, layers of electricallyphotosensitive particulate material which are more than one particlediameter in thickness may also be used.

One preferred form of the system of the present invention is illustratedin FIG. 2 wherein electrical information storage member 10 is shownsupported by substrate 15a, and at the surface of substrate 15a which isin contact with the semiconductor layer 14, a plurality of laterallyspaced electrodes 16 are in contact with the semiconductor layer 14. Inthe present invention the electrodes 16 are organized into a series ofgrid of electrode pairs, which at least partially surround discretesmall areas of the total area of the electrical information storagemember. Each of these discrete small areas may be considered to be arepository where a single bit of information may be stored in thestorage member of the present invention. The distance between electrodesof a single electrode pair, for example between electrode pair 16' ofFIG. 2, is quite small, and, for example, in the present invention maybe on the order of approximately 2 mils or 50 microns, as illustrated inFIG. 2. It will thus be appreciated that an extremely large number ofbits of information can be stored in a relatively small overall area ofthe advantageous electrical image storage members of the presentinvention.

The grid pattern in which the pairs of electrodes 16 appear in thesystem of FIG. 2 is perhaps more clearly illustrated in therepresentative area views of FIGS. 3A-3C, which schematically illustratevarious preferred embodiments of area grids in which said electrodepairs may be used. For example, in FIG. 3A, electrode pairs 17 are shownin the form of two spaced line electrodes having an open, substantiallyrectangular area 19 therebetween. It is the area approximately definedby the electrode pairs 17 and the space therebetween 19, which is anindividual bit of storage of information on the surface of the storagemember. As shown in FIG, 3A, adjacent rows of electrode pairs 16 appearin a grid-like pattern to thereby provide a large number of informationbits throughout the surface of the storage member.

In FIG. 3B the electrodes 16 which form electrode pairs 17 are each inan L-shaped configuration, with the two L-shaped electrodes of each pairinverted with respect to each other thereby defining approximatelyrectangular area 19 which is almost entirely surrounded by the electodes16 which form each of the electrode pairs 17. As will be more clearlyappreciated after reviewing the subsequent description of the operationof these electrode pairs, these mutually inverted L-shaped pairs whichalmost entirely surround the area 19, provide an electron pair systemwhich is preferable to that shown in FIG. 3A, because there is greaterliklihood that any information stored within an individual bit, asillustrated in FIG. 3B, will show response upon scanning of theindividual bits for retrieval of any information on the storage member.

FIG. 3C shows a still further embodiment of the grid of electrodes 16forming electrode pairs 17 which enclose bit-areas 19. Like the mutuallyinverted L-shaped electrode pairs illustrated in FIG. 3B, the concavelyfacing crescent or semicircular electrodes 16 of the electrode pairs 17illustrated in FIG. 3C almost completely enclose the bit-areas 19,thereby providing an effect similar to that provided by the electrodepair grid arrangement illustrated in FIG. 3B. It will be appreciatedthat the systems of FIG. 3B and 3C also minimize edge effects orelectrode end effects which would be more pronounced at the ends of theparallel spaced electrodes in the pairs 17 illustrated in FIG. 3A.

Another preferred embodiment of the electrical information storagemembers of the present invention is illustrated in FIG. 8 whereinstorage member 10 is supported on substrate 15b which is in contact withelectrode layer 13 at the opposite side of the member 10 from thesemiconductor layer 14. It will be appreciated that the memberillustrated in FIG. 8 is the same as the member illustrated in FIG. 1absent substrate 15a, while the member illustrated in FIG. 2 is similarto the member illustrated in FIG. 1 absent substrate 15b.

Materials suitable for use as substantially electrically insulatinglayer 11 in the electrical information storage members of the presentinvention include the materials disclosed for use as softenablesubstantially electrically insulating material in U.S. Pat. No.3,801,314, copending application Ser. No. 27,890, filed Apr. 13, 1970;as well as the materials suitable for use as a solvent solubleelectrically insulating layer in U.S. Pat. No. 3,520,681; and thedisclosures of those patents and application, respectively, are herebyexpressly incorporated by reference herein. A particularly preferredmaterial for use as the substantially electrical insulating material oflayer 11 is a custom synthesized 80/20 mol% copolymer of styrene andhexylmethacrylate having an intrinsic viscosity of about 0.179 dl/gm(when measured in toluene). The layer of substantially electricallyinsulating material 11 may be of any desired thickness, so long as thelayer of electrically photosensitive material 12 ia fully embeddedtherein. Insulating layer thicknesses of up to about 4 microns arepreferred, with insulating layer thicknesses of about 0.5 to about 2microns being particularly preferred.

Materials suitable for use as the electrically photosensitiveparticulate material 12 in the electrical information storage members ofthe present invention also include the photosensitive materialsdisclosed in the aforementioned U.S. Pat. Nos. 3,520,681 and 3,801,314.A particularly preferred electrically photosensitive material isselenium or a selenium alloy with arsenic, tellurium, antimony,thallium, bismuth, or mixtures thereof, such as arsenic triselenide, aswell as other materials include substantially pure amorphous selenium,which may include substantially pure amorphous selenium or amorphousselenium alloys doped with materials such as halogens. Other suitableelectrically photosensitive materials include phthalocyanines such asX-form metal-free phthalocyanine or Monolite Fast Blue GS, the alphaform of metal-free phthalocyanine, C.I. No. 74100, available from ArnoldHoffman Co;, Algol Yellow G.C. 1,2,5,6-di (c,c'-diphenyl)-thiazole-anthroquinone, C.I. No. 67300, available from GeneralDyestuffs; Light Cadmium Orange Concentrate, a cadmium selenide pigment,C.I. No. 77196, available from Imperial Color and Chemical Co.; IndofastBrilliant Scarlet Toner, 3, 4,9,10-bis[N,N'-(p-methoxyphenyl)-imido]-perylene, C.I. No. 71140, availablefrom Harmom Colors; Watchung Red B, a barium salt of1-(4'-methyl-5'-chloroazobenzene-2'-sulfonic acid)-2-hydroxy-3-naphthoicacid, C.I. No. 15865, available from duPont; as well as mixturesthereof, or composite particles containing more than one electricallyphotosensitive material is a binder of polyvinyl alcohol, polyvinylchloride, polyethylene, polyvinyl carbazole or other suitable material.The term "electrically photosensitive" as used herein means materialswhich show increased electrical conductivity when illuminated withelectromagnetic radiation, which includes materials which apparentlyallow selective relocation, of charge into, within, or out thereof, saidrelocation being affected by the action of light on the bulk or surfaceof the electrically photosensitive material when said material isexposed to activating electromagnetic radiation such as light. Theseeffects may include photoconductive affects, photoinjection,photoemission, photochemical effects, and others which cause theaforementioned selective relocation of charge.

In preferred embodiments of the electrical information storage membersof the present invention, the layer of electrically photosensitiveparticulate material 12 will comprise a mono-layer of particlessubstantially uniformly distributed throughout the surface area of thelayer of the substantially insulating material 11, with substantiallyall of the particles of electrically photosensitive material fullyembedded in, or surrounded by, electrically insulating material 11. Apreferred way for preparing such a layer of electrically photosensitivematerial in a layer of substantially electrically insulating material,is the vacuum evaporation vapor deposition technique disclosed in Goffeet al U.S. Pat. No.3,598,644, which is hereby expressly incorporated byreference herein. When one of these techniques is used with a preferredmaterial, such as selenium, a layer of particles of size generally lessthan about 1 micron, but within the range from about 0.01 to about 2.0microns is produced, and those particles are substantially entirelyembedded within the upper surface of a layer of electrically insulatingmaterial when preferred electrically insulating materials are used.

The electrode 13 may in various embodiments comprise any suitablematerial, but preferably comprises a material which is substantiallytransparent to activating electromagnetic radiation which activates theelectrically photosensitive particulate material 12. While the electrode13 may be applied directly onto the surface of substantially insulatingmaterial layer 11, as shown for example, in FIG. 2, the electrodematerial 13 is more typically applied upon the surface of anothersubstrate, for example such a substrate 15b as shown in FIG. 1 and FIG.8. The electrode may be any suitably transparent continuous conductivecoating including, for example, coatings of tin, indium oxide, aluminum,chromium, tin oxide, or any other suitable conductor. Such substantiallytransparent conductive coatings may be applied, for example, byevaporation or any other means onto either the surface of thesubstantially insulating material 11, or the surface of a substrate 15b.Where the electrode comprises a substantially transparent conductivelayer on a substrate, NESA glass, a tin oxide coated glass manufacturedby the Pittsburgh Plate Glass Company, is a commercially availableexample of a suitable transparent conductive electrode material. Anothersuch example is aluminized Mylar, a polyester film available fromduPont, overcoated with a thin aluminum layer which is about 50% visiblelight transmissive. The substrate 15a or 15b, may comprise any suitablematerial, but is preferably substantially electrically insulatingmaterials, such as glass or plastic. A number of such substrates aredisclosed in the aforementioned U.S. Pat. Nos. 3,520,681, and 3,801,314.In various embodiments, the substrates, and the electrical informationstorage members of the present invention may be used in any suitableform, including a web, foil, laminate, strip, sheet, coil, cylinder,drum, endless belt, endless mobius strip, circular disc, or the like.

The semiconductor layer 14 may comprise any suitable semiconductormaterial having a resistivity of at least a few hundred ohm-cm. Morespecifically, semiconductor materials having a resistivity in the rangeof about 500 ohm-cm to about 2000 ohm-cm. are preferred. Relatively wideband-gap semi-conductors may be used. Examples of suitable materialsinclude pure silicon, doped silicons, compounds of elements fromPeriodic Table Groups II and VI such as the oxides, sulfides orselenides of zinc and cadmium, compounds of elements from Periodic TableGroups III and V such as the arsenides or antimonides of gallium orindium, and others, these materials intended to be exemplary and notlimiting. The layer of semiconductor material 14 may be of any suitablethickness, with layers of thicknesses on the order of about 0.1 micron,for example layers in the range of about 3000 Angstroms (0.03 microns)to about 1 micron being particularly preferred. Such semiconductorlayers may be provided by any of the well known semiconductor coatingmeans, including the method wherein the semiconductor is vacuumevaporated onto a desired surface in a vacuum chamber wherein anelectron beam impinges upon a source of the semiconductor which isevaporated and subsequently deposited.

The small electrodes 16 which form the electrode pairs 16' and 17 shownin FIGS. 2 and 3A-3C, may be produced by any suitable means, but wellknown microprinting techniques are preferred wherein microscopicelectrodes of metallic material or metallic inks are provided on thesurface of a substrate, for example like substrate 15a shown in FIG. 2.Currently available microprinting techniques are capable of providingsuch printed electrodes, or printed circuitry, in such small sizes thata few hundred line pairs per millimeter may be distinctly printed.

From all of the foregoing it will therefore be appreciated that anelectrical information storage member such as that illustrated in FIG. 2can be produced by providing a substrate 15a, microprinting the desiredelectrodes or electrode pairs 16 and 16' thereon, overcoating theelectroded substrate with a semiconductor layer 14, over which layer ofsubstantially electrically insulating material 11 is coated into whichlayer of electrically photosensitive material 12 is embedded, and themember is completed by the addition of electrode 13 at the upper surfaceof substantially insulating layer 11.

Similarly, the advantageous electrical information storage members asillustrated in FIG. 8 may be provided by first coating a layer ofsubstantially electrically insulating material 11 on a temporarysubstrate and then embedding the layer of electrically photosensitivematerial 12 therein by one of the techniques discussed above herein,whereafter the layer of substantially electrically insulating material11 containing the layer of electrically photosensitive material 12 istransferred to an electroded substrate 15b having a conductor layer 13thereon by a contact transfer technique. For example a technique such asthat disclosed in Jones et al U.S. Pat. No. 3,770,554, the disclosure ofwhich is hereby expressly incorporated by reference herein, may be used.The member is then completed by overcoating the remaining exposedsurface of the layer of substantially insulating material 11 with asemiconductor layer 14.

Before discussing how the electrical information storage members of thepresent invention are believed to theoretically operate, it is useful todiscuss how electrical information is initially recorded in such anelectrical information storage member. In one mode, as illustrated inFIGS. 4A-4C, the member is electrically charged by connecting all of theelectrodes 16 to one side of a potential source 30, connecting theelectrode layer 13 to ground or the opposite pole of the source ofpotential (FIG. 4A), thereby creating a potential difference across thesubstantially electrically insulating layer 11, and then imagewiseexposing (FIG. 4B) the layer of electrically photosensitive material 12so that the electrically photosensitive particles 12 in areas exposedwith activating electromagnetic radiation 31 undergo their electricallyphotosensitive effect, forming an electrical latent image (FIG. 4C) inthe electrical information storage member of the present invention. Inthis method electrical information is stored in those areas which areimagewise exposed with activating electromagnetic radiation, and thatelectrical information is in the form of an electrical latent imagecorresponding to the imagewise exposure. This method of latently imagingsuch a member is described in more detail in U.S. Pat. application Ser.No. 327, filed Jan. 2, 1970, now abandoned.

Another method of storing electrical information in the storage memberof the present invention is a method wherein electrical information isselectively placed in the storage member through an address system usingthe microelectrodes 16 which form electrode pairs 17. In this mode asillustrated in FIGS. 6A-6C, overall electrode 13 is grounded or biasedto a potential of sign opposite to that to be applied to selectiveelectrode pairs 17, and the storage member is substantially uniformlyirradiated with activating electromagnetic radiation 32, as shown inFIG. 6A. Then, as shown in FIG. 6B, an electrical voltage pulse 34 isapplied to an electrode pair 17' thereby creating an electrical fieldacross the entire thickness of the storage member 10. The presence of anelectrical field across the entire thickness of the storage member 10,as well as the presence of activating electromagnetic radiation 32,allows the electrically photosensitive material 12 in areas 33 wheresuch fields are present to undergo its electrically photosensitiveeffect thereby storing information, again in the form of an electricallatent image, corresponding to the electrical voltage applied to theaddressed electrode pair 17' in area 33. The resultant storedinformation or electrical latent image is schematically illustrated ascharges trapped in area 33 of FIG. 6C, when the electrical circuitry isdisconnected

The theoretical operation of the information storage members illustratedin FIGS. 2 and 3A-3C, is schematically illustrated in more detail inFIG. 5. The state of the microelectronics art is such that printed gridpatterns such as those discussed with respect to FIGS. 2 and 3A-3C canreadily be prepared including leads to each of the electrodes of eachindividual electrode pair, and electrical address systems forselectively energizing or otherwise electrically connecting leads foreach individual electrode pair to an exterior source of energy ormonitor are also readily available. In the system of the presentinvention, the area of an electrical information storage member isscanned to selectively connect an electrical pulse source externallyacross the two electrodes which comprise each electrode pair 17, asillustrated in FIGS. 3A-3C, and FIG. 5. In conjunction with the pulsesource is a readout means which is a current detector for determiningwhen a current actually flows between two electrodes of an electrodepair 17 while the pulse source is connected between such a pair ofelectrodes. Local changes in resistivity of the semiconductor film in anelectrically imaged member in the inventive system are detected by thecurrent detector. When the detector shows that a flow of current inresponse to an applied pulse between two electrodes of an electrode pairis greater than detected current flow responses between other electrodepairs, this is an indication that electrical information is stored inthe bit of storage member surface defined by that electrode pair.

Significant current flows in response to an applied pulse will typicallyoccur in those areas of the member containing electrical informationtrapped therein. This is schematically illustrated in FIG. 5, where theelectrical information is indicated by the presence of charges,including charges induced in the semiconductor layer 14. The charges insemiconductor layer 14 are induced by the charges trapped in theelectrically photosensitive material 12, and the charges in thesemiconductor layer 14 provide a channel for the easy transport ofcharge carriers laterally in the semiconductor layer. The channelcurrents in the present invention are similar to those which occur insemiconductor layers in known MOS (metal-oxide-semiconductor) devices.It is the channel current which flows through this field induced channelwhich is detectable the current detector thereby providing a signalcorresponding to the information stored in an individual bit of area ofthe storage member. The information signal may be used in any way whichmay be desired. For example, corresponding information may be stored inanother sort of computer storage device, or that information may bereconstructed into a visible image corresponding to the latent image,for example on a computer addressed cathode ray tube system. It is thisinformation signal which represents the information retrieved from thestorage member, and that information is retrieved without destroying theinformation stored in the member itself. It will of course beappreciated that due to the very small scale of the areas of volumes ofmaterials involved in the system of a single electrode pair 17, that thechannel currents being detected in the present system are of quite smallmagnitude, i.e., typically less than one milliamp or in the microamprange.

Substantially the same methods of addressing the electrical informationstorage member as described in conjunction with FIGS. 4A-4C and 6A-6Cmay be used in conjunction with the member which does not include anelectrode 13. This method is illustrated in FIG. 7 wherein the functionof the electrode is taken by another means of providing an electricalfield across the thickness of the information storage member. In FIG. 7electrode 13 is replaced by electrostatic charges 18 substantiallyuniformly provided to the top surface of the layer of substantiallyelectrically insulating material 11 by passing a corona charging device19 over that surface. Corona charging systems and other suitablecharging systems are well known in the xerographic arts, and are furtherdescribed in the aforementioned U.S. Pat. Nos. 3,580,681 and 3,801,314.Despite the absence of an electrode 13, the presence of the electricallphotosensitive material 12, and the layer of semiconductive material 14,still provide the necessary effects for the member to function to storeand retrieve electrical information therein. Whether the storage memberincludes an electrode 13 as shown in FIGS. 4A-C and 6A-C, or does notinclude an electrode 13 as shown in FIG. 7, the foregoing systems foraddressing the storage member provide a relatively low cost storagemember and system for storing binary information, and if the addresssystem has the capability of providing differential magnitudes ofaddress pulse inputs, the system is capable of storing electricalinformation corresponding to such different magnitudes, therebyproviding another degree of freedom, and greatly increasing the totalcapacity of the storage system. Such different magnitudes of input, whenstored in the storage member are the electrical equivalent of differenttones or shades in a corresponding optical image.

As previously indicated the electrically photosensitive material in thestorage members of the present invention is present in the form of alayer of particles of size generally less than about 1 micron, andwithin a range from about 0.01 to about 2.0 microns. If the electricallyphotosensitive material particles have, for example, a diameter of about0.3 microns, approximately 10⁹ such particles occur in a squarecentimeter of surface area of the storage member. With such largenumbers of potential individual information storage units, it should beclear that the size of information storage bits in the storage membersof the present invention is principally limited by the state of the artof the microprinting techniques by which the electrodes 16 and electrodepairs 17, as well as their lead circuitry, are produced. For example, ifelectrode pairs are spaced by approximately 50 microns, and the size ofthe individual storage bit is therefore about 50 microns or 2 milssquare, the information in the present storage members may have aresolution of about 10 lp/mm, and the storage capacity of the film wouldbe about 7.5 million bits per square foot. However, it is known thatimaging members suitable for use in the migration imaging systemdescribed in the aforementioned U.S. Pat. Nos. 3,580,681 and 3,801,314,have a resolution capacity of almost 1000 lp/mm, which is evidence thatresolution capabilities of the members of the present system for storingelectrical information is orders of magnitude higher than that which canbe achieved by a system including the aforementioned 50 micron squarebits. This capacity necessarily contributes to the economical advantageof the present system wherein tremendous amounts of information may bestored in a very small surface area of an electrical information storagemember which is itself quite economical to produce.

From this disclosure it should now be clear that electrical informationcorresponding to visible images can be stored in the members of thepresent invention at photographic speeds. Such images are sometimesreferred to as electrical latent images, and such electrical latentimages can be retrieved, or read out from the storage members of thepresent invention, and that reading out does not necessarily destory thelatent electrical information in the storage member. Indeed theelectrical information or electrical latent images stored in members ofthe present invention are substantially permanently stored therein, andare not destroyed, even by using the imaged or information containingmembers in room lighted environments, a capability which theaforementioned migration imaging members did not have. Because of thelasting quality of electrical information or latent images stored in thestorage members of the present invention, additional electricalinformation or electrical latent images may be added to the informationor images already existing in the storage member, limited only by theavailable surface area of the member.

The electrical information storage members of the present invention maybe produced in another embodiment and used in still another fashion. Asillustrated in FIG. 8, the member 10 may comprise substantiallyelectrically insulating layer 11 containing layer of electricallyphotosensitive material 12 supported on substrate 15b with electrode 13at the surface of substantially insulating layer 11 which facessubstrate 15b. In this embodiment the semiconductor layer 14 comprisesthe exterior surface of the member opposite the substrate 15b. Thestorage member in FIG. 8 is particularly useful when information is tobe retrieved therefrom using an electron beam system generallydesignated 20 in FIG. 8. Electron beam system 20 is schematicallyillustrated as including an electron gun 21, an accelerator screen 22,focus electrode 23 and deflector yoke 24 which are all provided withelectrical leads by which they are connected to suitable electricalcircuitry to operate the electron beam system. When such an electronbeam scans an electrical information storage member with the electronbeam impinging upon the semiconductor layer 14, the intensity of thebeam is monitored by a read out coil 25 positioned near the acceleratorgrid 22. This system can be compared with the system illustrated in FIG.5 by considering that when a greater current will be accepted by acertain portion of the storage member, an increase in magnitude in theelectron beam which will be accepted by the storage member is anindication corresponding to information stored in that portion of thestorage member illustrated in FIG. 8. In this way, the electron beamretrieves information stored in the member, and produces an electricalsignal in the readout means which corresponds to that storedinformation. As in the case explained in conjunction with FIG. 5, oncethe information is retrieved through such a readout means, it may bestored for example in a computer storage system, or it may bereconstructed into a visible image corresponding to the informationstored in the storage member, or used for any other suitable purpose.

Still further, the system illustrated in FIG. 8 may actually be used toaddress information into the storage member in a manner similar to thatdiscussed in conjunction with FIGS. 4A-C, 5, 6A-c and 7. In the case ofFIG. 8, the information is provided to the storage member in the form ofan electron beam which is directed toward a portion of the member whereit is desired to store certain information, and electrode 13 is at thesame time appropriately biased to create an electrical field across thethickness of the member while the member is substantially uniformlyirradiated with activating electromagnetic radiation, thereby allowingthe electrically photosensitive material 12 to undergo its electricallyphotosensitive effect in those areas where a field is generated betweenelectrode 13 and an impinging electron beam. For example, if a storagemember of thickness of about 1-2 μm is used and a biasing field of about1 × 10⁵ V/cm to about 5 × 10⁵ V/cm is usually used to create a latentimage therein by applying a voltage of 20 to 50 volts, the surfacecharge density is about 1 × 10¹¹ e⁻ /cm² to about 5 × 10¹¹ e⁻ /cm², andif the area of each electrode pair cell is about 25 × 10⁻⁶ cm², thecharge per cell is about 1 × 10⁷ e⁻. Hence if a corresponding electronbeam is focused to impinge upon an area of about 50 sq. μm, and has acurrent density of about 0.1 mA, the beam should remain on eachelectrode pair cell area for about 1/10 μsec. to provide the desiredelectrical input.

In this way electrical information corresponding to the informationaddressed to the member by the electron beam is stored in the memberitself. As described with the previous systems, the member of thepresent invention is capable of storing not only binary information dueto the presence or absence of electrical information at various bits orsurface area elements of the storage member, but that information mayalso contain further information corresponding to the intensity andduration of the electron beam by which the information is originallyaddressed to the storage member.

The following examples further specifically define the electricalinformation storage system of the present invention. The parts andpercentages are by weight unless otherwise indicated. The examples beloware intended to illustrate various preferred embodiments of the novelelectrical information storage system.

EXAMPLE I

An electrical information storage member according to the presentinvention is fabricated by microprinting about 60 mm × 60 mm (2 1/2 in.× 2 1/2 in.) frames of complimentary inverted L-shaped electrodes, asillustrated in FIG. 3C, onto a roll of about 70 mm wide, about 5 milthick Mylar polyester resin available from duPont. While any suitablemicroprinting method may be used, one method includes first usingoptical reduction and photo-etching to print electrically conductivelead stripes of about 10 to 20 microns in width across the width of thefilm, about 16 stripes being in each millimeter thereof for a total ofabout 1000 stripes per 60 mm frame. Next a thin Mylar i.e., about 0.5mil thick, film is perforated in rows of extremely small holes, i.e.,about 0.2 mil diameter, and in a pattern which matches theaforementioned printed stripes, on the thicker Mylar, except that thethin Mylar is about 60 mm wide, and the holes therein are at intervalsof 16 holes per mm, or about 1000 holes per row across the 60 mm widefilm. Any other suitable method may be used to produce such holes, andone such method includes automatically punching those holes by the useof a pulsating and oscillating laser beam which instantaneously meltsaway the Mylar. The perforated thin film is then laminated onto theprinted thicker film in such a way that the rows of holes match thestripes printed onto the thicker film. One way of achieving thismatching is to do it automatically by optical reference point adjustmentusing a laser beam. After lamination the more narrow and thin filmsurface is printed with rows of electrically conductive stripesextending in directions perpendicular to the stripes on the thickerMylar, and formed into L-shaped electrode patterns, wherein one of eachcomplimentary pair of L-shaped electrodes is electrically connected tothe stripes on a thicker Mylar film thereby providing separateelectrical contacts for each of the electrodes of any complimentary pairof L-shaped electrodes in the system. The 60 mm × 60 mm frames ofmicro-printed electrode pairs include about one million, 50 micron × 50micron cells, each surrounded by a pair of complimentary, relativelyinverted, L-shaped electrodes.

A semiconductor film is then deposited over the micro-printed array ofelectrodes to a thickness of more than about 500 Angstroms by vacuumdepositing silicon thereon in a vacuum atmosphere wherein a source ofsilicon is bombarded by an electron beam, and a vacuum is maintained atabout 10⁻⁶ Torr in order to avoid oxidization of the depositedsemiconductor. The deposition of the semiconductor material can be madecontinuously along the entire strip of film being fabricated in order tocover all frames on the strip in one continuous operation.

The semiconductor coated micro-printed film is then coated with an about0.5 to 1 micron thick film of substantially electrically insulatingthermoplastic material comprising an 80/20 hexylmethacrylate/polystyrenecopolymer (Tg of about 55° C) which is roller coated over thesemiconductor layer and then oven dried in a partial vacuum.

A layer of electrically photosensitive material is then vacuumevaporated into a substantially monolayer configuration near the uppersurface of the layer of substantially electrically insulatingthermoplastic material, this particulate layer of electricallyphotosensitive material comprising amorphous selenium vacuum evaporatedby the technique disclosed in U.S. Pat. No. 3,598,644. The particles ofelectrically photosensitive selenium in the monolayer are of size ofabout 0.1 to about 0.5 microns in diameter.

Thereafter a partially transparent conductive electrode film of aluminumof thickness of about 500 Angstroms is continuously deposited on theupper surface to complete an image storage member having a cross sectionlike that illustrated in FIG. 2. The aluminum electrode can be vacuumevaporated onto the member in the same apparatus for vacuum evaporatingthe selenium as described in the previous step. The resultant electrodelayer will allow optical transmission of visible light to an extent ofabout 50%, but is continuously electrically conductive.

EXAMPLE II

Electrical information storage members made according to Example I haveinformation recorded thereon by photo-electrical means, and subsequentlyretrieved therefrom, as follows. A film containing the about 60 mm × 60mm frames of microprinted electron pairs overcoated with the otherelements of the inventive electrical information storage members isloaded into a camera apparatus similar to that described in BlackertU.S. Pat. No. 3,528,355 wherein the framing device for locating a frameof film to be exposed therein is provided with X and Y arrays of contactpoints which make contact with corresponding leads to the printedcircuit micro-electrodes in the storage member when the storage memberis positioned therein. The contact points are electrically connectedwith a solid-state switching device, and when images are to beselectively addressed to the film by photographic means, all of thepairs of electrodes are connected together by the solid-state switchingdevice and a positive voltage in the range of about 10 to about 50 voltsis applied thereto, while the aluminum electrode of the storage memberis grounded. The shutter of the camera is opened for an instant toimagewise expose the film with light intensity which in various areasmay range from about 0.1 to about 100 milliergs/cm² sec. For the storagemember wherein the electrically photosensitive material comprisesselenium, blue light exposure is particularly preferred, and is often asubstantial component of the output of CRT displays which may berecorded by the present system. After exposure, the applied bias voltageis disconnected, and the film advanced until the next frame is placedwith its electrode leads in contact with the contact points in thecamera apparatus. The exposed frame of the film exhibits no visibleimage, and after the bias voltage is removed from all electrodes may begrounded and thereafter the film retains no photographic sensitivityuntil it is again biased.

The same apparatus may be used for addressing information into thestorage member by electrical techniques rather than photographic oroptical techniques, by placing the desired frame of the film in theframing device of the camera apparatus with its electrical leads incontact with the contact points in the camera apparatus. The electricalinformation is addressed into each individual cell by applying a pulsedpositive bias voltage of magnitude of about 30 volts to both of theelectrodes of each pair, while the aluminum electrode on the top surfaceof the storage member is grounded, and while the shutter is openedexposing the entire surface of the frame of the storage member to lightenergy of about 10⁻² milliergs/cm² sec. In this way electricalinformation is addressed into the particular area controlled by theelectrodes through which the bias is applied. When the shutter is closedand the film advanced, the storage member contains information in eachof the areas of the member where the electrode pairs were so biased.Once again the film exhibits no visible image and after groundingretains no photographic sensitivity until again biased. The film can bestored in a room environment, or for even longer life can be stored in asealed container.

Information stored in a member by either the primarily photographicmeans, or the primarily electrical means, described above, is retrievedby placing the film back in the camera apparatus, ensuring that theelectrode leads in contact points in the frame portion of the cameraapparatus are properly registered and maintaining the shutter in closedposition. The solid state switching device is then used to send voltagepulses between each of the pairs of electrodes in each bit of the framearea. A test pulse of magnitude of several volts is applied between thetwo electrodes for a very short duration i.e., about a few tens ofnanoseconds (10⁻⁸ sec), when using these members where the semiconductorlayer comprises a few hundred Angstroms of silicon. The pulse currentacross a one Kohm resistor in series in the circuit across the twoelectrodes of the pair produces a signal which is typically on the orderof about 1 millivolt where no information is in the bit of the storagemember, to several hundred millivolts for a bit of the storage memberwhich is fully charged with electrical information. The signalsresultant from the foregoing detection system are fed into apulse-analyzer, the output of which may be displayed or transmitted, orcompared with specific information stored elsewhere. The total accesstime to the information stored in each frame of film is on the order ofa few milliseconds.

Thus it is seen that by using the address and retrieval systems of thepresent invention, it is possible to obtain an exact duplicate of anyparticular frame by retrieving the information therefrom and recordingthe same information onto a second film by one of the methods of thepresent invention. Furthermore, the information so retrieved is noterased from its original storage member in the process, and it ispossible to duplicate only a portion of a total frame of information,thereby selectively omitting certain portions of the total picture orinformation in a single frame by deliberately supressing the outputvoltage pulses of cells in those areas where the information is to beomitted. In this way it is possible to obtain a copy of the informationor image in a frame with effectively erased portions thereof. Thistechnique may be useful in segmenting or combining various compositearrays of photographic information or other data.

EXAMPLE III

Where the electrical information storage member is to be used in anelectron beam address and retrieval system, the microprinting of pairedelectrodes and their lead stripes as described in Example I above, isunnecessary. In this case, the semiconductor film may simply be vacuumdeposited on a layer of readily soluble material, such as gelatin,whereupon the layer of substantially electrically insulatingthermoplastic material is overcoated, and the monolayer of amorphousselenium particles vacuum evaporated therein, all as described inExample I. The surface of the film into which the selenium particleswere vacuum evaporated is then laminated to an aluminized Mylar surface,the aluminum of which corresponds to electrode 13, and the Mylarsubstrate of which corresponds to layer 15b, as shown in FIG. 8. Thealuminized Mylar substrate is sufficiently transparent to light for thepurposes of this invention. The soluble material upon which thesemiconductor film was first formed is then dissolved, in this case bydissolving the gelatin film with water.

Information is then addressed into the storage member by mounting thestorage member in a chamber which can be evacuated. The chamber is alsoequipped with electron beam system similar to that illustrated in FIG.8. Alternatively, rather than mounting the film in a vacuum chamber, thesemiconductor surface of the film may be placed tightly on the window ofa special electron beam generating cathode ray tube which has a suitablefront window, comprising for example a thin strip of beryllium metal ora fiber optic plate through either of which the electron beam may stilleffectively address the storage member. For example, where therelatively low density beryllium metal plate is used, a 25 KeV electronbeam can penetrate about 5 microns (0.2 mil), and a 40 KeV electron beamcan penetrate about 12.5 microns (0.5 mil).

Regardless of whether the vacuum chamber or special CRT system are used,the electron beam is used to write information in the form of negativecharges in the semiconductor surface of the storage member, and when thestorage member is uniformly illuminated with activating electromagneticradiation, the storage member traps an electrical latent image thereindue to the local electrical fields generated by the charges placed onthe semiconductor by the electron beam. If the members in use in thisexample where the layer of substantially electrically insulatingthermoplastic materials is about 1 micron thick, it is typicallynecessary to develop a local field of 20 to 50 volts across the filmthickness in order to electrically latently image the member. Suchfields typically require surface charge densities of about 5 × 10¹¹electrons per cm.². Where the electron beam can be focused to an area ofabout 10 microns in diameter, which would correspond to a resolution ofabout 50 lp/mm, and operated at a total electron flux of about 100microampheres, the electron beam may be scanned at a rate up to about 10microseconds per centimeter, while still providing the desired surfacecharge density to the member. Where the electron beam must also traversea window on the front of a special CRT tube, the writing speed is a feworders of magnitude slower because of the attenuation of the electrondensity by the window.

In addition to selectively addressing individual portions of the area ofthe storage member of the present invention, the electron beam systemmay also be used in conjunction with a photographic address system. Inthis case the storage member and the electron beam system are kept in adark atmosphere, and electron beam system is used to uniformly scan thesurface of the film to charge the semiconductor layer. In this mode itis good practice to not sharply focus the beam so that the scanninglines are not well defined and charging is more uniform. At the momentof charging, which typically can be completed in less than 1millisecond, the film is exposed to the desired light image through thealuminized Mylar substrate side thereof, thereby causing theelectrically photosensitive selenium particles to undergo theirelectrically photosensitive effect trapping an electrical latent imagein the storage member.

The images placed on a storage member by any of the foregoing means areretrieved by again placing the imaged storage member in a vacuum chamberor against the window of the special CRT tube electron beam system, anda low intensity, tightly focused electron beam is used to scan thesemiconductor surface thereof. The electron gun is operated at low anodevoltage, for example, less than one Kv. The electron beam intensityvariation is monitored with a small grid coil as shown in FIG. 8, andthe differences in intensity monitored by the grid coil produce a signalwhich corresponds to the information and magnitude thereof stored in theparticular portion of the storage member upon which the scanningelectron beam is momentarily focused. The location of the electron beamon the storage member is synchronized with the signal from the grid coildetector by synchronizing means like those used in common televisionreceivers, which operate from the deflection yoke of the electron gun.

Although specific components, proportions and arrangements of elementshave been stated in the above description of preferred embodiments ofthis invention, other equivalent components and arrangements of elementsmay be used with satisfactory results and various degrees of quality, orother modifications may be made herein to synergize or enhance theconstruction of the invention to thereby increase its utility. It willbe understood that such changes of details, materials, arrangements ofparts, and uses of the invention described and illustrated herein, areintended to be included within the principles and scope of the claimedinvention.

What is claimed is:
 1. A method of addressing electrical informationinto an electrical information storage member, comprising, providing anelectrical information storage memer comprising a solid layer ofsubstantially electrically insulating material containing a layer ofparticulate electrically photosensitive material, a semiconductor layercontacting one surface of said layer of substantially electricallyinsulating material, a substantially transparent electrode layer ofelectrically conductive material contacting the opposite surface of saidlayer of substantially electrically insulating material and a pluralityof electrode pairs contacting said semiconductor layer,substantiallyuniformly exposing the entire layer of electrically photosensitivematerial with activating electromagnetic radiation, and placing anelectrical field across the thickness of the member in desired areas ofthe member by biasing the electrodes of selected electrode pairs withrespect to said electrode layer, thereby addressing electricalinformation into said desired areas corresponding to said selectedelectrode pairs.
 2. A method of addressing electrical information intoan electrical information storage member, comprising:providing anelectrical information storage member comprising a solid layer ofsubstantially electrically insulating material containing a layer ofparticulate electrically photosensitive material, a semiconductor layercontacting one surface of said layer of substantially electricallyinsulating material, and a substantially transparent electrode layer ofelectrically conductive material contacting the opposite surface of saidlayer of substantially electrically insulating material, substantiallyuniformly exposing the entire layer of electrically photosensitivematerial with activating electromagnetic radiation, and placing anelectrical field across desired areas of said member by impinging anelectron beam onto the surface of the semiconductor layer in desiredareas, thereby addressing electrical information into said deisred areasof the member.
 3. The method of claim 2, wherein impingement with theelectron beam is carried out when said electrode layer is connected to asource of positive charge.
 4. The method of claim 3 wherein theelectrode layer is grounded.
 5. The method of claim 3 wherein theelectrode layer is positively biased.